Add fail2ban DB index management and socket-based path resolution

- New get_fail2ban_db_path() in setup_service resolves DB path from configured socket path
- New ensure_fail2ban_indexes() creates missing performance indexes on bans table
- Call ensure_fail2ban_indexes on every startup before first ban query
- Remove completed tasks from Docs/Tasks.md
- Update Docs/PERFORMANCE.md with index findings

Docs/PERFORMANCE.md

@@ -95,4 +95,52 @@ Use `EXPLAIN QUERY PLAN` to verify index usage:
 EXPLAIN QUERY PLAN SELECT ip, COUNT(*) FROM history_archive WHERE timeofban >= ? GROUP BY ip;
 ```
 
-Expected: `USING INDEX idx_history_archive_timeofban` in the output.
+Expected: `USING INDEX idx_history_archive_timeofban` in the output.
+
+---
+
+## Fail2ban Database Indexes
+
+BanGUI reads from fail2ban's SQLite database (`/var/run/fail2ban/fail2ban.db`). Query performance degrades without appropriate indexes.
+
+### Current fail2ban bans Indexes
+
+Fail2ban creates these indexes on the `bans` table:
+- `bans_jail_timeofban_ip` — composite (jail, timeofban, ip)
+- `bans_jail_ip` — composite (jail, ip)
+- `bans_ip` — single (ip)
+
+**Missing**: standalone index on `timeofban` alone.
+
+### BanGUI Automatic Index Creation
+
+On startup, BanGUI calls `ensure_fail2ban_indexes()` to add missing indexes idempotently:
+
+```python
+# From fail2ban_db_utils.py
+CREATE INDEX IF NOT EXISTS idx_bans_timeofban_desc ON bans(timeofban DESC);
+```
+
+This improves queries like:
+```sql
+SELECT * FROM bans WHERE timeofban >= ? ORDER BY timeofban DESC;
+```
+
+### Verifying Index Usage
+
+Check if a query uses the index:
+```sql
+EXPLAIN QUERY PLAN SELECT * FROM bans WHERE timeofban >= 1700000000 ORDER BY timeofban DESC;
+-- With index: SEARCH USING INDEX idx_bans_timeofban_desc
+-- Without: SCAN TABLE bans
+```
+
+### Adding Indexes to Migrations
+
+For BanGUI's own `history_archive` table, indexes go in migrations via `_ Migration.add_table_indexes()`:
+
+```python
+def _add_history_archive_indexes(m: Migration) -> None:
+    m.add_index("history_archive", ["timeofban"], unique=False, if_not_exists=True)
+    m.add_index("history_archive", ["jail", "timeofban"], unique=False, if_not_exists=True)
+```